Quintuple Carbon Steel Core Coil for Highly Focused Transcranial Magnetic Stimulation in Small Animals

Transcranial magnetic stimulation (TMS) is a non-invasive neuromodulation technique used to regulate the synaptic activity of neurons, bringing effective treatment to different neurological and psychiatric disorders. Its induced E-field needs to be focused enough to avoid unwanted overstimulation out of the target region. TMS in small animals like rodents [1] is highly constrained [2,3,4], since most of its studies use equipment with power and coils not designed for small animals. Using FEM in ANSYS Maxwell, we obtained results for a customized array of five double-winding solenoids to restrict the stimulation to areas as small as 1mm². Each solenoid of 2X25 turns includes a core with V-shape tip sharpening made of steel 1010 of 2T of saturation B at 4×10⁴ A/m. E and B fields were calculated 4.00 mm below the coil (cortical layer 5/6 in rat brains) with a single non-repetitive pulse of current of 5kA at 2.5kHz. The achieved 100V/m in a small target of 1mm² suggests the suitability of the coil to perform in-vivo experimentation on rodents.

References:
[1] J. Boonzaier et al, 2019. DOI: 10.1111/ner.13025
[2] J. Selvaraj et al, 2018. DOI: 10.1109/TMAG.2018.2846521.
[3] M. T. Wilson et al, 2018. DOI: 10.1088/2057-1976/aab525.
[4] I. P. de Sousa et al, 2018. DOI: 10.7717/peerj.5034